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Number
Lets you work with numeric values. The Number object is an object wrapper for primitive numeric values.
创建源
The Number constructor:
new Number(value);
参数
描述
The primary uses for the Number object are:
The properties of Number are properties of the class itself, not of individual Number objects.
Navigator 4.0: Number(x) now produces NaN rather than an error if x is a string that does not contain a well-formed numeric literal. For example,
x=Number("three");
document.write(x + "<BR>");
prints NaN
属性概览
方法概览
示例
示例 1. The following example uses the Number object's properties to assign values to several numeric variables:
biggestNum = Number.MAX_VALUE
smallestNum = Number.MIN_VALUE
infiniteNum = Number.POSITIVE_INFINITY
negInfiniteNum = Number.NEGATIVE_INFINITY
notANum = Number.NaN
示例 2. The following example creates a Number object, myNum, then adds a描述 property to all Number objects. Then a value is assigned to the myNum object's描述 property.
myNum = new Number(65)
Number.prototype.description=null
myNum.description="wind speed"
属性
MAX_VALUE
The maximum numeric value represen表 in JavaScript.
描述
The MAX_VALUE property has a value of approximately 1.79E+308. Values larger than MAX_VALUE are represented as "Infinity".
Because MAX_VALUE is a static property of Number, you always use it as Number.MAX_VALUE, rather than as a property of a Number object you created.
示例
The following code multiplies two numeric values. If the result is less than or equal to MAX_VALUE, the func1 function is called; otherwise, the func2 function is called.
if (num1 * num2 <= Number.MAX_VALUE)
func1()
else
func2()
MIN_VALUE
The smallest positive numeric value represen表 in JavaScript.
描述
The MIN_VALUE property is the number closest to 0, not the most negative number, that JavaScript can represent.
MIN_VALUE has a value of approximately 2.22E-308. Values smaller than MIN_VALUE ("underflow values") are converted to 0.
Because MIN_VALUE is a static property of Number, you always use it as Number.MIN_VALUE, rather than as a property of a Number object you created.
示例
The following code divides two numeric values. If the result is greater than or equal to MIN_VALUE, the func1 function is called; otherwise, the func2 function is called.
if (num1 / num2 >= Number.MIN_VALUE)
func1()
else
func2()
NaN
A special value representing Not-A-Number. This value is represented as the unquoted literal NaN.
描述
JavaScript prints the value Number.NaN as NaN.
NaN is always unequal to any other number, including NaN itself; you cannot check for the not-a-number value by comparing to Number.NaN. Use the isNaN function instead.
You might use the NaN property to indicate an error condition for a function that should return a valid number.
示例
In the following example, if month has a value greater than 12, it is assigned NaN, and a message is displayed indicating valid values.
var month = 13
if (month < 1 || month > 12) {
month = Number.NaN
alert("Month must be between 1 and 12.")
}
参看
isNaN, parseFloat, parseInt
NEGATIVE_INFINITY
A special numeric value representing negative infinity. This value is displayed as "-Infinity".
描述
This value behaves mathematically like infinity; for example, anything multiplied by infinity is infinity, and anything divided by infinity is 0.
Because NEGATIVE_INFINITY is a static property of Number, you always use it as Number.NEGATIVE_INFINITY, rather than as a property of a Number object you created.
示例
In the following example, the variable smallNumber is assigned a value that is smaller than the minimum value. When the if statement executes, smallNumber has the value "-Infinity", so the func1 function is called.
var smallNumber = -Number.MAX_VALUE*10
if (smallNumber == Number.NEGATIVE_INFINITY)
func1()
else
func2()
POSITIVE_INFINITY
A special numeric value representing infinity. This value is displayed as "Infinity".
描述
This value behaves mathematically like infinity; for example, anything multiplied by infinity is infinity, and anything divided by infinity is 0.
JavaScript does not have a literal for Infinity.
Because POSITIVE_INFINITY is a static property of Number, you always use it as Number.POSITIVE_INFINITY, rather than as a property of a Number object you created.
示例
In the following example, the variable bigNumber is assigned a value that is larger than the maximum value. When the if statement executes, bigNumber has the value "Infinity", so the func1 function is called.
var bigNumber = Number.MAX_VALUE * 10
if (bigNumber == Number.POSITIVE_INFINITY)
func1()
else
func2()
prototype
Represents the prototype for this class. You can use the prototype to add properties or methods to all instances of a class. For information on prototypes, see Function.prototype.
方法
toString
Returns a string representing the specified object.
语法
toString()
toString(radix)
参数
描述
Every object has a toString method that is automatically called when it is to be represented as a text value or when an object is referred to in a string concatenation.
You can use toString within your own code to convert an object into a string, and you can create your own function to be called in place of the default toString method.
You can use toString on numeric values, but not on numeric literals:
// The next two lines are valid
var howMany=10
document.write("howMany.toString() is " + howMany.toString() + "<BR>")
// The next line causes an error
document.write("45.toString() is " + 45.toString() + "<BR>")
For information on defining your own toString method, see the Object.toString method.
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